Device and method for adjusting and controlling actual supplied amount of urea entering an exhaust system

ABSTRACT

A device for adjusting and controlling the actual supplied amount of urea entering an exhaust system comprises an electronic control unit ( 1 ), a compressed air supply device ( 2 ), a urea storage device ( 3 ), a compressed air control device ( 4 ), a metering pump or a metering valve ( 5 ), a spray nozzle ( 6 ), a main pipeline ( 7 ), a urea pipeline ( 8 ), and a urea control device ( 9 ). The urea control device ( 9 ) is in communication with the electronic control unit ( 1 ) and controls the actual supplied amount of urea injected into the exhaust system from the spray nozzle according to the starting time point and the finishing time point. A method for adjusting and controlling the actual supplied amount of urea entering an exhaust system is also disclosed. The present device and method effectively prevent the excessive urea from being injected into the exhaust system, and enable the original exhaust system to match with stricter emission standards through a low cost improvement.

FIELD OF TECHNOLOGY

The present invention relates to the control system for internalcombustion engine, especially a device for adjusting and controlling theactual supplied amount of urea entering an exhaust system and theadjusting and controlling method thereof.

BACKGROUND OF ART

Internal combustion engines may be categorized into two types, namelygasoline engines and diesel engines, which are characterized with theirrespective advantages due to the different work mechanisms. The gasolineengines are lighter with less vibration and enhanced smoothness whilethe diesel engines work more efficiently with a 30% cut-down in the fuelconsumption and a high torque enabling higher performance at a lower RPMand high power. Generally, the diesel engines have been expected forgreat prospects for a great many of benefits despite of some evidentdefects. The emission pollution of internal combustion engines includescarbon monoxides (CO), hydrocarbons (HC), nitrogen oxides (NOx) andparticulate matters (PM). The emission pollution of gasoline engines aremainly CO and HC that ternary catalysts have been turned to be asolution. The emission pollution of diesel engines are mainly NOx andPM. The pollution caused by NOx, a hard problem for a long time, hasbeen found a bit easier to deal with in recently years by means ofExhaust Gas Recirculation (EGR) and Selective Catalytic Reduction (SCR).

NOx and PM are found to be on the opposite side of the pollutionproblem. The NOx pollution mainly derives from the heat generated fromthe high combustion temperature, that leads to the oxidation ofNitrogen. In order to reduce the generation of PM, the temperature isfurther heated after full burning of diesel leading to the increased NOxpollution, and vice versa. During EGR a proportion of the exhaust gas isallowed to return into the intake air inlet. The proportion of oxygencomprised in the intake air is decreased, accompanied by the reducedgeneration of NOx but increased PM. The application of EGR will alsocause higher fuel consumption and thus higher cost. It can be seen thatalthough EGR is advantaged in that no additional substance is involvedin its process but the effect is rather limited. During SCR NOx reactswith ammonia to produce nitrogen and water, the process of whichrequires the aid of a catalyst. Ammonia is known for difficult storageand handling due to its instability and toxic. To deal with thisproblem, the urea solution is sprayed into the upstream of the SCRcatalyst. The hydrolysis of urea will take place at the high combustiontemperature producing a mixture of ammonia, carbon dioxide and water.The released ammonia then enters the catalyst chamber to react with NOxand get rid of the pollution. The SCR technology is expected withgreater prospects for its higher efficiency in NOx conversion, exceptthat the additional provision of urea solution leaves room forimprovement. DPFs refer to diesel particulate filters, which tend toclog up due to the absorption of particulates to an amount. Theregeneration is achieved through removing the absorbed carbonparticulates by burning at a high temperature. However, in China,currently the high content of sulfur in diesel has caused theregeneration of the particulates of sulfur compounds unable to achieve.The DPF has to be replaced anew at a cost. This reality is one of thereasons for tightening the emission standards in China. DOCs refer toDiesel Oxidation Catalysts that play an active role in the process ofconverting carbon particulates into carbon dioxide.

The modern after-treatment system integrates multiple systems, whereasSCR constitutes the core of the after-treatment system for dieselengines. The emission standards for diesel engines include the Europeanstandards and the U.S. standards. In China, the European standards havebeen referred to for reference. Currently the national emissionstandards III, which follow the European standards III, are in generalpractice in China and are believed to be soon substituted with thenational emission standards IV, where in some major cities of Chinanational emission standards V have been put into effect. The majority ofEuropean are practicing standards V with a number of major citiespracticing standards VI, which is planned for a full launch in 2014. TheEuropean standards III are considered rather out-of-date, which may beachieved by EGR technology. SCR technology would be necessary to meetwith the European standards IV. Compared with European standards IV, theEuropean standards V have been tightened for the emission of NOx whileno changes have been made to the PM emission. The PM emission issignificantly reduced by half and NOx to one-fifth of the previousstandards in the European standards VI.

The SCR technology is rather complex. In theory, to improve theconversion rate of exhaust gas can be realized through the utilizationof either an increased amount or massive of catalyst or increased amountof urea. However, it is not that simple in practical. Firstly, theincreasing of catalyst to use means even higher cost and also greatervolume, both of which will become unacceptable. Secondly, the emissionof ammonia due to the extra urea, called ammonia leaks, involvespollution itself with its toxicity and strong smell. It is stated in theemission standards that the average ammonia leak should be kept downbelow 10 ppm with the maximum value no more than 25 ppm. Therefore, thekey point underlying the SCR technology is focused on injection ofproper amount of urea at the proper timing so as to reach a higherconversion rate while managing the ammonia leaks within limits, in otherwords, the urea injection strategy. Nonetheless, the actual suppliedamount of urea is influenced by a number of factors, such as the amountof urea piped from the urea chamber being hard to control to becompletely equivalent to that injected into the exhaust system, and thateven the most optimized injection strategy has only been able to live upto the average value standard yet without success for the maximumrestriction. In the prior arts, targeting at the fulfillment of NOxemission standard as well as ammonia leaks, such means as an increasedmass of SCR catalyst, first lowering NOx by EGR technology combined withSCR, or other alternative methods have been used in an attempt, still nohigh hopes for the practice or popularization of either of which due tothe high cost and failure in complying with the European standards VI.

The present invention provides a device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system and theadjusting and controlling method thereof, giving a more precise methodin urea injection that will prevent the over injection of urea andfurther lower the cost of SCR process.

SUMMARY OF THE INVENTION

Provided in the present invention is a device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, which comprises an electronic control unit, a compressed airsupply device, a urea storage device, a compressed air control device, ametering pump or a metering valve, a spray nozzle, a main pipeline and aurea pipeline; the said electronic control unit is connected with theinternal combustion engine of the exhaust system, used for thecollection of the performance parameters of the internal combustionengine and calculation of the target supplied amount of urea in theexhaust system and further the determination of the starting time pointand finishing time point; the said urea storage device is provided forstoring the urea; the said compressed air supply device is connected tothe main pipeline; the said compressed air control device is installedat the connection point between the compressed air supply device and themain pipeline, and communicates with the electronic control unit tocontrol the flow rate of the compressed air into the main pipeline; athrough hole is formed in the middle section of the main pipeline; thesaid urea storage device is connected to the through hole by the ureapipeline; the said metering pump or the metering valve, installed to theurea pipeline, communicates with the electronic control unit, whichcontrols the volume of the urea provided by the urea storage device intothe main pipeline; the outlet of the main pipeline extends into theexhaust system; the said spray nozzle is installed at the said outlet ofthe main pipeline so that the urea is introduced into the exhaust systemthrough spraying; the urea mixes with the compressed air in the mainpipeline. With references to FIG. 1 and FIG. 10, the present devicefurther comprises an urea control device, which is installed to the mainpipeline, and communicates with the electronic control unit; the saidurea control device is controlled in such a way so that the compressedair is provided into the main pipeline when the urea is controlled toenter the exhaust system, causing the urea in the main pipeline to begiven into the spray nozzle by the compressed air and further enter theexhaust system in the spay-like form; when the urea is controlled to beheld from entering the exhaust system, the compressed air is providedinto the spray nozzle without passing through the main pipeline, causingthe urea in the main pipeline to be held from entering the spray nozzleand from entering the exhaust system.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 10, the said urea control device furthercomprises a three-way valve and an branch airway; the said three-wayvalve is installed to the section of the main pipeline between thecompressed air control device and the through hole; the inlet of thethree-way valve is connected to the compressed air control device whilethe first outlet is connected to the main pipeline and the second outletis connected to the said branch airway; the other end of the branchairway is connected to the main pipeline with the connecting pointlocated between the through hole and the spray nozzle; the three-wayvalve communicates with the electronic control unit; when the urea iscontrolled to enter the exhaust system, the three-way valve connects thecompressed air supply device to the main pipeline, allowing thecompressed air to enter the main pipeline; when the urea is controlledto be held from entering the exhaust system, the three-way valveconnects the compressed air supply device to the branch airway, allowingthe compressed air to enter the spray nozzle by the branch airway.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 3, FIG. 5 and FIG. 6, the said urea controldevice is controlled in such a way so that when the urea is controlledto be held from entering the exhaust system, the compressed air isprevented from entering the spray nozzle, thereby preventing the ureafrom entering the spray nozzle and further into the exhaust system.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 3, the said urea control device furthercomprises a control valve the said control valve is installed to themain pipeline between the urea pipeline and the spray nozzle; thecontrol valve communicates with the electronic control unit, whichswitches on and off the connection between the main pipeline 7 and thespray nozzle by shifting the control valve between an open position anda close position.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 5 and FIG. 8, the said urea control devicefurther comprises a bypass channel and a bypass control valve; the saidbypass channel is connected to the main pipeline with the connectingpoint located between the urea pipeline and the spray nozzle; the saidbypass control valve is installed to the bypass channel and communicateswith the electronic control unit, the electronic control unit shifts thebypass control valve to an open position for allowing the compressed airto enter the external atmosphere through the bypass channel and shiftsthe bypass control valve to a close position for allowing the compressedair to enter the spray nozzle.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 8, the connecting point of one end of thebypass channel with the main pipeline is located at upstream of thecontrol valve; by switching the control valve to the close position andthe bypass control valve to the open position, the compressed air isallowed to enter the bypass channel; whereas by switching the controlvalve to the open position and the bypass control valve to the closeposition, the compressed air is allowed to enter the spray nozzle.

Provided in the present invention the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to FIG. 6 and FIG. 8, the other end of the bypasschannel is further connected to the urea storage device; by switchingthe bypass control valve to the open position, the compressed air isallowed to enter the urea storage device through the bypass channel.

Also provided in the present invention is a method provided foradjusting and controlling the actual supplied amount of urea entering anexhaust system, wherein the said method comprises:

Step 1: collecting the performance parameters of the exhaust system andthe internal combustion engine, and making calculation of the targetsupplied amount of urea in the exhaust system and further thedetermination of the starting and finishing time points;

Step 2: the compressed air supply device providing the compressed airinto the main pipeline, while the urea storage device providing theaqueous urea into the main pipeline through the urea pipeline, so thatthe urea and the compressed air mix in the main pipeline; both theprovided volume of the urea and the flow rate of the compressed air aredetermined according to the target supplied amount of urea;

Step 3: with references to the devices as depicted in FIG. 1 and FIG.10, when the urea is allowed to enter the exhaust system, the compressedair is provided into the main pipeline by referring to the starting timepoint, so that the urea in the main pipeline is fed into the spraynozzle by the compressed air and further provided into the exhaustsystem in the spray-like form; when the urea is controlled to be heldfrom entering the exhaust system, the compressed air is provided intothe spray nozzle by referring to the finishing time point withoutpassing through the main pipeline, so that the urea in the main pipelineis held from being fed into the spray nozzle and further into theexhaust system.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 10, the said Step 3 furthercomprises: when the urea enters the exhaust system, the three-way valveconnects to the compressed air supply device to the main pipeline,allowing the compressed air to enter the main pipeline; when the urea iscontrolled to be held from entering the exhaust system, the three-wayvalve connects the compressed air supply device to the branch airway,allowing the compressed air to enter the spray nozzle through the branchairway 95.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 10, when the target suppliedamount of urea is below the pre-set threshold, the three-way valve iscontrolled to connect to the main pipeline intermittently so that thecompressed air is provided into the main pipeline intermittently,causing the remaining urea in the main pipeline to enter the spraynozzle.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 3, FIG. 5, FIG. 6 and FIG. 8,the said Step 3 is replaced by following: when the urea is allowed toenter the exhaust system, the compressed air is provided into the mainpipeline by referring to the starting time point, so that the urea inthe main pipeline is fed into the spray nozzle by the compressed air andfurther provided into the exhaust system in the spray-like form; whenthe urea is controlled to be held from injecting into the exhaustsystem, the compressed air is prevented from entering the spray nozzle,so that the urea is held from being fed into the spray nozzle andfurther into the exhaust system.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 3, the said Step 3 comprisesinstalling the control valve to the main pipeline; the control valve isshifted between an open position and a close position to switch on andoff the connection between the main pipeline and the spray nozzle.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 5, FIG. 6 and FIG. 8, thesaid Step 3 comprises installing a bypass channel and a bypass controlvalve outside the pipeline; when the bypass control valve is shifted tothe open position, the compressed air is allowed to enter the externalatmosphere through the bypass channel, whereas when the bypass controlvalve is shifted to the close position, the compressed air is allowed toenter the spray nozzle.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 6, the said Step 3 furthercomprises that the connecting point of the bypass channel with the mainpipeline is located upstream of the control valve; by switching thecontrol valve to the close position and the bypass control valve to theopen position, the compressed air is allowed to enter the bypasschannel; whereas by switching the control valve to the open position andthe bypass control valve to the close position, the compressed air isallowed to enter the spray nozzle.

Provided in the present invention the method for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, by referring to the device of FIG. 6 and FIG. 8, the said Step 3further comprises that the other end of the bypass channel is furtherconnected to the urea storage device; by switching the bypass controlvalve to the open position, the compressed air is allowed to be fed intothe urea storage device through the bypass channel.

The present invention put forward a solution which is effective incontrolling the maximum amount of ammonia leak, giving an actualsupplied amount of urea closer to the target supplied amount and makesfull use of the SCR catalyst. The existing urea supply system is revisedin the present invention, in which the ammonia leak is reduced at lowcost while managing to fulfill even stricter emission standards.

DESCRIPTIONS OF DRAWINGS

FIG. 1 shows the structure of the present device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem.

FIG. 2A shows the flowchart of the method for adjusting and controllingthe actual supplied amount of urea of the devices depicted in FIG. 1 andFIG. 10; FIG. 2B shows the flowchart of the method for adjusting andcontrolling the actual supplied amount of urea of the devices depictedin FIG. 5, FIG. 6 and FIG. 8.

FIG. 3 shows the structure of the device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system in Example1.

FIG. 4 shows the graph of square waves representing the controlledactual supplied amount of urea in Example 1.

FIG. 5 shows the structure of the device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system in Example2.

FIG. 6 shows a preferred structure of the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem in Example 2.

FIG. 7 shows the graph of square waves representing the controlledactual supplied amount of urea in Example 2.

FIG. 8 shows the structure of the device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system in Example3.

FIG. 9 shows the graph of square waves representing the controlledactual supplied amount of urea in Example 3.

FIG. 10 shows the structure of the device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system in Example4.

FIG. 11 shows the graph of square waves representing the controlledactual supplied amount of urea in Example 4.

FIG. 12 shows an alternative structure of the device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem in Example 4.

FIG. 13 shows the graph of square waves representing the actual suppliedamount of urea entering the exhaust system in the prior art.

FIG. 14 shows yet another alternative structure of the device foradjusting and controlling the actual supplied amount of urea entering anexhaust system in Example 4.

FIG. 15 shows yet another alternative structure of the device foradjusting and controlling the actual supplied amount of urea entering anexhaust system in Example 4.

EMBODIMENTS OF THE INVENTION

The present invention is further described in details with reference tothe following embodiments and drawings. References can be made to thegeneral knowledge and common knowledge of the art for the determinationof the processes, conditions and methods involved in the implementationof the present invention. Unless otherwise specified, the scope of thepresent invention is not intended to be limited to the disclosedembodiments.

Numerous factors including the delay in data collection and datacalculation, the distance from urea tank to exhaust system and the flowrate of the compressed air have brought out inevitable time lag betweenthe time point at which the aqueous urea is injected to the mainpipeline and the time point at which the urea enters exhaust system. Asis shown in FIG. 13, such time lag leads to both inadequate actualsupplied amount of urea at the starting time point as compared with thetarget amount and excess of actual supplied urea at the finishing timepoint. The former has become a restricting factor for the efficiency ofpollution reduction while the latter leads to the failure in complyingwith the emission standards due to over-dose urea. Focusing on theadjustment and control of the actual supplied amount of urea entering anexhaust system, the present invention introduces a urea control devicewhich controls the actual amount of urea injected into the spray nozzleand that into the exhaust system prior to the urea entering the exhaustsystem, which tackles the issue of over-dosing of the supplied urea.

FIG. 1 indicates the structure of the present device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem, which comprises an electronic control unit 1, a compressed airsupply device 2, a urea storage device 3, a compressed air controldevice 4, a metering pump or a metering valve 5, a spray nozzle 6, amain pipeline 7, a urea pipeline 8 and a urea control device 9. Theelectronic control unit 1 is connected with the internal combustionengine of the exhaust system, used for the collection of the performanceparameters of the internal combustion engine and calculation of thetarget supplied amount of urea in the exhaust system and further thedetermination of the starting and finishing points. The compressed aircontrol device 4 is installed at the connection point between thecompressed air supply device 2 and the main pipeline 7, and communicateswith the electronic control unit 1 to control the flow rate of thecompressed air into the main pipeline 7. A through hole is formed in themiddle section of the main pipeline 7. The urea storage device 3 isconnected to the through hole by the urea pipeline 8. The metering pumpor the metering valve 5, installed to the urea pipeline 8, communicateswith the electronic control unit 1, which controls the volume of theaqueous urea provided by the urea storage device 3 into the mainpipeline 7 according to the target supplied amount of urea. The aqueousurea mixes with the compressed air in the main pipeline 7, the outlet ofwhich extends into the exhaust system. The spray nozzle 6 is installedat the outlet of the main pipeline 7 so that the urea is introduced intothe exhaust system through spraying. The urea control device 9,installed to the main pipeline 7, communicates with the electroniccontrol unit 1, which controls the actual supplied amount of ureaentering the exhaust system through the spray nozzle 6 within the periodof time set out by the starting and finishing time points.

FIG. 2A represents the flow chart of the method provided in the presentinvention for adjusting and controlling the actual supplied amount ofurea entering an exhaust system based on the described device, whichcomprises:

Step 1: the electronic control unit 1 collects the performanceparameters of the exhaust system and the internal combustion engine,makes calculation of the target supplied amount of urea in the exhaustsystem and further the determination of the starting and finishing timepoints;

Step 2: the compressed air supply device 2 provides the compressed airinto the main pipeline 7, while the urea storage device 3 provides theaqueous urea into the main pipeline 7 through the urea pipeline 8, sothat the urea and the compressed air are mixed in the main pipeline 7;the volume of the urea is controlled by the metering pump or themetering valve 5 installed to the urea pipeline 8, while the flow rateof the compressed air is controlled by the compressed air control device4 installed to the main pipeline 7; both the compressed air controldevice 4 and the metering pump or the metering valve 5 communicate withthe electronic control unit 1 which sends out controlling instructionsaccording to the target supplied amount of urea;

Step 3: when the urea is allowed to enter the exhaust system, thecompressed air is provided into the main pipeline 7 by referring to thestarting time point, so that the urea in the main pipeline 7 is fed intothe spray nozzle 6 by the compressed air and further provided into theexhaust system in the spray-like form; when the urea is controlled to beheld from entering into the exhaust system, the compressed air isprovided into the spray nozzle 6 by referring to the finishing timepoint without passing through the main pipeline 7, so that the urea inthe main pipeline 7 is held from being fed into the spray nozzle 6 andfurther into the exhaust system; or alternatively as indicated by FIG.2B,

when the urea is allowed to enter the exhaust system, the compressed airis provided into the main pipeline 7 by referring to the starting timepoint, so that the urea in the main pipeline 7 is fed into the spraynozzle 6 by the compressed air and further provided into the exhaustsystem in the spray-like form; when the urea is controlled to be heldfrom entering the exhaust system, the compressed air is alternativelyprevented from flowing into the spray nozzle 6 by referring to thefinishing time point, so that the urea is held from being fed into thespray nozzle 6 and further into the exhaust system.

The structure of the present device and the mechanism and function willbe discussed in further details below in combination with a plural ofexemplary embodiments.

Example 1

As shown in FIG. 3 is the structure of the present device for adjustingand controlling the actual supplied amount of urea entering an exhaustsystem. The urea control device 9 further comprises a control valve 91.The control valve 91 is installed to the main pipeline 7, morespecifically, for example installed to the section between the ureapipeline 8 and the spray nozzle 6. The control valve 91 is controlled bythe electronic control unit 1, which switches on and off the connectionbetween the main pipeline 7 and the spray nozzle 6 by shifting thecontrol valve 91 between an open position and a close position. With theconnection switched on, the compressed air and the urea mix together toflow through the spray nozzle 6 and into the exhaust system; while withthe connection switched off, the compressed air and the urea still mixin the main pipeline 7 but can find no way into the spray nozzle 6under, which prevents the excess of urea fed into the exhaust system.

The flowchart of the present device is explained in further details withreference to FIG. 4. The electronic control unit 1 collects theperformance parameters of the exhaust system and the internal combustionengine, makes calculation of the target supplied amount of urea in theexhaust system and further the determination of the starting time pointand the finishing time point.

As illustrated by the first square wave in FIG. 4, the metering pump orthe metering valve 5 allows the aqueous urea into the main pipeline 7 atthe starting time point, the mixture of urea and compressed air isprovided into the spray nozzle 6 and further into the exhaust system;certain lag out is bound to arise between the actual time point at whichthe urea enters the exhaust system and the starting time point, due tothe time required for the movement of urea and the process for mixing;the control valve 91 is shifted to the close position at the finishingtime point under the control of the electronic control unit 1, causingthe connection of the main pipeline 7 with the spray nozzle 6 to switchoff, rendering the flow rate of the compressed air at the spray nozzle 6to nil; under such circumstance, the urea is prevented from entering thespray nozzle 6 together with the compressed air, thus preventing theurea from further entering the exhaust system post the finishing timepoint and thereby avoid the excessive urea being sprayed into theexhaust system. The remaining urea is reserved within the main pipeline7.

As illustrated by the second square wave in FIG. 4, the metering pump orthe metering valve 5 continues to allow the aqueous urea into the mainpipeline 7 at the starting time point; at the same time the controlvalve 91 is shifted to the open position to switch on the connectionfrom the main pipeline 7 to the spray nozzle 6; the left-over urea inthe main pipeline 7 from the last square wave is provided into the spraynozzle 6 together with the compressed air and further enters the exhaustsystem. This process makes up the shortage of urea due to the inevitablelate supply at the beginning of the second square wave; the controlvalve 91 is shifted to the close position at the finishing time pointunder the control of the electronic control unit 1 to avoid excessiveurea being sprayed into the exhaust system.

As illustrated by the third square wave in FIG. 4, which indicates anoccasion where the operating condition of the internal combustion engineis subjected to a sudden change which leads to a decreasing in thetarget supplied amount of urea, and the target supplied amount of ureacalculated by the electronic control unit 1 is below the pre-setthreshold, that is evidently fewer than the target amount of ureacompared against the previous two square waves; under such circumstance,the control valve 91 is shifted to the open position, leading theleft-over urea in the main pipeline 7 from the last square wave togetting into the spray nozzle 6 and further entering the exhaust system;temporary excess of actual supplied amount of urea entering the exhaustsystem may occur within a short period of time in the case when theamount of the left-over urea from the last square wave may be more thanthe target amount of urea at present square wave; the control valve 91is shifted to the close position at the finishing time point under thecontrol of the electronic control unit 1 to avoid excessive urea beingsprayed into the exhaust system.

As can be seen from the above, the provision of urea is controlled insuch a manner that urea will not enter the exhaust system at a timelater than the finishing time point, with a small amount of shortage ofurea supply at the starting time point and a possible small amount ofover-dosing in the event of a sudden change to the operating condition.By comparison with FIG. 13, it can be seen that the introduction ofcontrol valve 91 to adjust and control the actual supplied amount ofurea will contribute to the reduction on urea overdosing, favourable forstricter emission standards at a relatively lower cost. Possiblesolution for the excess issue under sudden change to the operatingcondition will be described in the following Example 3.

Example 2

As shown in FIG. 5 is the structure of the present device for adjustingand controlling the actual supplied amount of urea entering an exhaustsystem. The urea control device 9 further comprises a bypass channel 92and a bypass control valve 93. The bypass channel 92 is connected to themain pipeline 7 with the connecting point located between the ureapipeline 8 and the spray nozzle 6. The bypass control valve 93 isinstalled to the bypass channel 92 and communicates with the electroniccontrol unit 1, which shifts the bypass control valve 93 between an openposition and a close position. With the bypass control valve 93 in itsclose position, the urea and the compressed air mix together in the mainpipeline 7 to flow through the spray nozzle 6 and into the exhaustsystem; in the otherwise open position, the remained urea mixed with thecompressed air in the main pipeline 7 is discharged with the compressedair through the bypass channel 92, due to the lower pressure in thebypass channel 92 than the exhaust back pressure at the spray nozzle 6,avoiding excessive urea to enter the exhaust system with the compressedair.

In a further improvement for the prevention of excessive urea emission,the piping structure is further reconstructed. As shown by FIG. 6, thebypass channel 92 is connected to the urea storage device 3 so that theremained urea in the main pipeline 7 will recycle to the urea storagedevice 3 with the compressed air for later use.

The flowchart of the present device is explained in further details withreference to FIG. 7. The electronic control unit 1 collects theperformance parameters of the exhaust system and the internal combustionengine, makes calculation of the target supplied amount of urea in theexhaust system and further the determination of the starting andfinishing time points.

As illustrated by the first square wave in FIG. 7, with the bypasscontrol valve 93 in its close position, the metering pump or themetering valve 5 allows the aqueous urea into the main pipeline 7 at thestarting time point, the mixture of urea and compressed air is providedinto the spray nozzle 6 and further into the exhaust system; certain lagout is bound to arise between the actual time point at which the ureaenters the exhaust system and the starting time point, due to the timerequired for the movement of urea and the process for mixing; the bypasscontrol valve 93 is shifted to the open position at the finishing timepoint under the control of the electronic control unit 1, causing thecompressed air to purge the remained urea in the main pipeline 7 intothe bypass channel 92 for recovery as a result of the exhaust backpressure at the spray nozzle 6 being higher than the pressure in thebypass channel 92. The urea is thus prevented from further entering theexhaust system post the end time point and thereby avoid the excessiveurea being sprayed into the exhaust system.

As illustrated by the second square wave in FIG. 7, the metering pump orthe metering valve 5 continues to allow the aqueous urea into the mainpipeline 7 at the starting time point; at the same time the bypasscontrol valve 93 is shifted to the close position; since the remainedurea in the main pipeline 7 has been recovered, the lag out of ureasupply at the starting time point will occur as it does in theconventional urea supply operation; the bypass control valve 93 isshifted to the open position at the finishing time point under thecontrol of the electronic control unit 1, causing the compressed air topurge the remained urea in the main pipeline 7 into the bypass channel92 for recovery.

As illustrated by the third square wave in FIG. 7, which indicates anoccasion where the operating condition of the internal combustion engineis subjected to a sudden change which leads to a decreasing in thetarget supplied amount of urea, as the amount of left-over urea in themain pipeline 7 remain to be the same as the amount at the finishingtime point of the last square wave, it will not cause the excess ofactual supplied amount of urea as that in Example 1 to switch off thebypass control valve 93 at the starting time point under the instantoperation condition, while the shortage of urea supply will duplicate asin the last two square waves; the bypass control valve 93 is shifted tothe open position at the finishing time point under the control of theelectronic control unit 1, causing the compressed air to purge theremained urea in the main pipeline 7 into the bypass channel 92 forrecovery.

As can be seen from the above, the provision of urea is controlled insuch a manner that urea will not enter the exhaust system at a timelater than the finishing time point, with a small amount of shortage ofurea supply at the starting time point. By comparison with FIG. 13, itcan be seen that the introduction of control valve 91 to adjust andcontrol the actual supplied amount of urea will contribute to thereduction on urea overdosing, favourable for stricter emission standardsat a relatively lower cost. Although the shortage of the actual suppliedamount of urea may be more severe than Example 1, improvement can beobserved in terms of the handling of the actual urea supply excess. Afurther preferred implementation is provided in the following Example 3based on the combination of the previous Examples 1 and 2.

Example 3

As shown in FIG. 8 is the structure of the present device for adjustingand controlling the actual supplied amount of urea entering an exhaustsystem. The urea control device 9 further comprises a control valve 91,a bypass channel 92 and a bypass control valve 93. The control valve 91is installed to the main pipeline 7, more specifically, for exampleinstalled to the section between the urea pipeline 8 and the spraynozzle 6. The bypass channel 92 is connected to the main pipeline 7 withthe connecting point located between the urea pipeline 8 and the spraynozzle 6. The bypass control valve 93 is installed to the bypass channel92. Both the control valve 91 and the bypass control valve 93communicate with the electronic control unit 1, which shifts the controlvalve 91 and the bypass control valve 93 between their respective openpositions and close positions.

The flowchart of the present device is explained in further details withreference to FIG. 9. The electronic control unit 1 collects theperformance parameters of the exhaust system and the internal combustionengine, makes calculation of the target supplied amount of urea in theexhaust system and further the determination of the starting andfinishing time points.

As illustrated by the first square wave in FIG. 9, with the bypasscontrol valve 93 in its close position, the metering pump or themetering valve 5 allows the aqueous urea into the main pipeline 7 at thestarting time point, the mixture of urea and compressed air is providedinto the spray nozzle 6 and further into the exhaust system; certain lagout is bound to arise between the actual time point at which the ureaenters the exhaust system and the starting time point; the control valve91 is shifted to the close position at the finishing time point underthe control of the electronic control unit 1, causing the connection ofthe main pipeline 7 with the spray nozzle 6 to switch off, rendering theflow rate of the compressed air at the spray nozzle 6 to nil; under suchcircumstance, the urea is prevented from entering the spray nozzle 6together with the compressed air, thus preventing the urea from furtherentering the exhaust system post the finishing time point and therebyavoid the excessive urea being sprayed into the exhaust system. With thebypass control valve 93 in its close position, the remaining urea isreserved within the main pipeline 7.

As illustrated by the second square wave in FIG. 9, with the bypasscontrol valve 93 in its close position, the metering pump or themetering valve 5 allows the aqueous urea into the main pipeline 7 at thestarting time point; at the same time the control valve 91 is shifted tothe open position to switch on the connection of the main pipeline 7with the spray nozzle 6; the left-over urea in the main pipeline 7 fromthe last square wave is provided into the spray nozzle 6 together withthe compressed air and further enters the exhaust system. This processmakes up the shortage of urea due to the inevitable late supply at thebeginning of the second square wave; the control valve 91 is shifted tothe close position at the finishing time point under the control of theelectronic control unit 1 to avoid excessive urea being sprayed into theexhaust system.

As illustrated by the third square wave in FIG. 9, in which theoperating condition of the internal combustion engine is subjected to asudden change which leads to a decreasing in the target supplied amountof urea, both the control valve 91 and the bypass control valve 93 areshifted to the open position at the starting time point; the left-overurea in the main pipeline 7 from the last square wave is dischargedthrough the bypass channel 92 for recovery under the exhaust backpressure at the spray nozzle 6; the bypass control valve 93 is thenshifted to the close position after the brief recovery, causing theaqueous urea given by the urea storage device 3 that mixes with thecompressed air to enter the spray nozzle 6; the over dosing of urea intothe exhaust system issue due to the sudden change in the operationcondition in Example 1 is thus settled despite a certain amount of lagout; the control valve 91 is shifted to the close position at thefinishing time point under the control of the electronic control unit 1to avoid excessive urea being sprayed into the exhaust system.

As can be seen from the above, the provision of urea is controlled insuch a manner that urea will not enter the exhaust system at a timelater than the finishing time point, with a small amount of shortage ofurea supply at the starting time point yet significant improvement isobserved compared to Example 2.

Example 4

Significant improvements have been demonstrated in the controlling ofthe actual supplied amount of urea in Examples 1-3. However, thecompressed air to be given to the spray nozzle 6 will be cut off, whichgive rises to the deposition of urea within the spray nozzle 6 andfurther the condensation of urea under the combustion temperature ofexhaust system and finally causing the spray nozzle 6 to clog. A morepreferred Example 4 is provided herewith addressing the above issue forfurther adapting to industrial production and application.

As shown in FIG. 10 is a structure diagram for the device for adjustingand controlling the actual supplied amount of urea entering an exhaustsystem. The urea control device 9 comprises a three-way valve 94 and anbranch airway 95. The three-way valve 94 is installed to the section ofthe main pipeline 7 between the compressed air control device 4 and thethrough hole. The inlet of the three-way valve 94 is connected to thecompressed air control device 4 while the first outlet thereof isconnected to the main pipeline 7 and the second outlet thereof isconnected to the branch airway 95. The other end of the branch airway 95is connected to the main pipeline 7 with the connecting point locatedbetween he urea pipeline 8 and the spray nozzle 6. The three-way valve94 communicates with the electronic control unit 1, which switches thethree-way valve 94 among its positions. When the compressed air controldevice 4 is connected to the main pipeline 7, the compressed air isprovided by the compressed air supply device 2 into the main pipeline 7to mix with the urea, which is thereby sprayed into the exhaust system.When the compressed air control device 4 is connected to the branchairway 95, the compressed air is provided by the compressed air supplydevice 2 into the branch airway 95 and further enters the spray nozzle 6directly.

The flowchart of the present device is explained in further details withreference to FIG. 11. The electronic control unit 1 collects theperformance parameters of the exhaust system and the internal combustionengine, makes calculation of the target supplied amount of urea in theexhaust system and further the determination of the starting andfinishing time points.

As illustrated by the first square wave in FIG. 11, the three-way valve94 is controlled by the electronic control unit 1 in such a way so thatthe compressed air control device 4 is connected to the main pipeline 7,the metering pump or the metering valve 5 allows the aqueous urea intothe main pipeline 7 at the starting time point, the mixture of urea andcompressed air is provided into the spray nozzle 6 and further into theexhaust system; certain lag out is bound to arise between the actualtime point at which the urea enters the exhaust system and the startingtine point; the three-way valve 94 is controlled by the electroniccontrol unit 1 at the finishing time point so that the compressed aircontrol device 4 is connected to the branch airway 95, the compressedair is given directly into the spray nozzle 6 bypassing the mainpipeline 7; the compressed air alone instead of a mixture with the ureais sprayed into the exhaust system through the spray nozzle 6, so thatan excessive amount of urea is prevented from being injected into theexhaust system while the spray nozzle 6 is also prevented from cloggingthrough constant purging; the metering pump or the metering valve 5 hasbeen held from feeding more urea, with no left-over urea mixed with thecompressed air in the main pipeline 7, which will not deposit and enterthe spray nozzle 6 in the absence of pressure difference to cause oversupply of urea; the remaining urea is reserved within the main pipeline7.

As illustrated by the second square wave in FIG. 11, the metering pumpor the metering valve 5 allows the aqueous urea into the main pipeline 7at the starting time point; at the same time the three-way valve 94 iscontrolled by the electronic control unit 1 so that the compressed aircontrol device 4 is connected to the main pipeline 7; the left-over ureain the main pipeline 7 from the last square wave is provided into thespray nozzle 6 together with the compressed air and further enters theexhaust system. This process makes up the shortage of urea due to theinevitable late supply at the beginning of the second square wave; thethree-way valve 94 is controlled by the electronic control unit 1 at thefinishing time point so that the compressed air control device 4 isconnected to the branch airway 95, the compressed air is given directlyinto the spray nozzle 6 bypassing the main pipeline 7, avoiding theexcessive urea being sprayed into the exhaust system.

As illustrated by the third square wave in FIG. 11, in which theoperating condition of the internal combustion engine is subjected to asudden change which leads to a decreasing in the target supplied amountof urea, at the starting time point the three-way valve 94 is controlledby the electronic control unit 1 to switch at certain frequency back andforth between connecting the compressed air control device 4 to the mainpipeline 7 and to the branch airway 95, so that the compressed air isprovided into the main pipeline 7 intermittently, avoiding too muchleft-over of urea from the last square wave to bring about the oversupply of urea into the exhaust system as is the case in Example 1; atthe finishing time point the three-way valve 94 is controlled by theelectronic control unit 1 so that the compressed air control device 4 isconnected to the branch airway 95, the compressed air is given directlyinto the spray nozzle 6 bypassing the main pipeline 7, avoiding theexcessive urea being sprayed into the exhaust system.

As can be seen from the above, the provision of urea is controlled insuch a manner that urea will not enter the exhaust system at a timelater than the finishing time point, with a small amount of shortage ofurea supply at the starting time point only in the first round ofoperation. Compared with Examples 1-3 as well as the prior arts,provided in the present invention is the introduction of an branchairway by the main pipeline 7, a three-way valve to shift and controlthe amount of urea supplied by the spray nozzle 6, achieving to adjustand control the actual supplied amount of urea to overcome the oversupply issue while preventing the spray nozzle 6 from clogging up.Improvement has been made in the present invention at a lower cost forthe existing exhaust system to conform to stricter emission standards.

The scope of the present invention is not limited to the four examplesas described above. All the variations based on the inventive concept ofthe present invention within the reasonable prediction of those skilledin the art shall be incorporated into the scope of the presentinvention. The disclosure of the present invention also include anycombination of any of the four examples described above. For example,the bypass channel 92 and the bypass control valve 93 of Example 2 maybe introduced into Example 3, so that the left-over urea in the mainpipeline 7 in Example 4 may be further recovered by employing theadjusting and controlling method as in Example 3 with the use of thebypass channel 92 and the bypass control valve 93.

With reference to FIG. 12, provided is yet another embodiment ofimplementation of the present invention, in which the three-way valve 94is substituted with a three-way pipeline free of the control by anycontrolling valve. The compressed air is provided into both the mainpipeline 7 and the branch airway 95 from the compressed air controldevice 4. The control valve 91 is installed to the section of the mainpipeline 7 between the connecting points respectively connected to thebranch airway 95 and the urea pipeline 8. The control valve 91communicates with the electronic control unit 1, which shifts thecontrol valve 91 between an open position and a close position to allowfor or prevent the compressed air downstream movement within the mainpipeline 7. To avoid the accumulation of the urea solution at theconnecting point of the main pipeline 7 and the branch airway 95, thecompressed air is continuously provided through the branch airway 95.

With the control valve 91 in the open position, the compressed airenters both the main pipeline 7 and the branch airway 95, where aproportion of the compressed air mixes with the urea in the mainpipeline 7 before entering the spray nozzle 6 while another proportionenters the spray nozzle 6 by way of the branch airway 95, the urea issprayed into the exhaust system by spray nozzle 6. When the controlvalve 91 is switched to the close position, the compressed no longerenters the main pipeline 7 but still enters the branch airway 95 andfurther into the spray nozzle 6. As a result of the constant flow of thecompressed air in the branch airway 95, the accumulation of the ureasolution at the connecting point of the branch airway 95 and the mainpipeline 7 is purged into the exhaust system by the compressed airflowing out of the branch airway 95.

With reference to FIG. 14, provided is yet another embodiment ofimplementation of the present invention, in which the three-way valve 94is substituted with a one-way valve 96 and a one-way valve 97. Theone-way valve 96 is installed to the main pipeline 7 with the one-wayvalve 97 to the branch airway 95. Both the one-way valve 96 and theone-way valve 97 communicate with the electronic control unit 1, whichshifts the one-way valve 96 and the one-way valve 97 between their openpositions and close positions to allow for or prevent the flowing ofcompressed air into the main pipeline 7 or the branch airway 95. Theemployment of a pair of mutually exclusive valves in the presentembodiment to replace the three-way valve 94 improves the flexibility ofthe system by the independent controlling of the valves.

As shown in FIG. 14, with the compressed air control device 4 in theopen position, the one-way valve 96 is switched open while the one-wayvalve 97 close, where the compressed air enters the main pipeline 7giving a mixture with the urea in within which enters the spray nozzle 6that sprays the urea into the exhaust system; with the compressed aircontrol device 4 in the close position, the one-way valve 96 is switchedclose while the one-way valve 97 open, where the remaining compressedair enters the spray nozzle 6 by way of the branch airway 95. The oversupply of urea into the exhaust system is avoided in this way by thecompressed air entering the spray nozzle 6 bypassing the main pipeline7.

In the above embodiment, the compressed air control device 4 is anoptional part for installation. The compressed air control device 4 mayremain to be turned on during operation. Alternatively, the compressedair control device 4 may be removed, as shown in FIG. 15 the structureof device. When the one-way valve 96 is switched open and the one-wayvalve 97 close, the compressed air enters the main pipeline 7 giving amixture with the urea in within which enters the spray nozzle 6 thatsprays the urea into the exhaust system. When the one-way valve 96 isswitched close while the one-way valve 97 open, the compressed airenters the spray nozzle 6 by way of the branch airway 95. The oversupply of urea into the exhaust system is avoided this way by thecompressed air entering the spray nozzle 6 bypassing the main pipeline7. Additionally, the accumulation of the urea solution at the connectingpoint of the branch airway 95 and the main pipeline 7 is purged into theexhaust system by the compressed air flowing out of the branch airway95, as a result of the constant flow of the compressed air in the branchairway 95.

The scope of the invention shall not be limited to the embodiments asdescribed above. Those variations and merits that are readilypredictable to those skilled in the art shall also be incorporated intoscope the present invention, as defined by the set of claims attachedtherewith.

1. A device for adjusting and controlling the actual supplied amount ofurea entering an exhaust system, comprising an electronic controlunit(1), a compressed air supply device(2), a urea storage device(3), acompressed air control device(4), a metering pump or a meteringvalve(5), a spray nozzle(6), a main pipeline(7) and a urea pipeline(8);the said electronic control unit(1) is connected with the internalcombustion engine of the exhaust system, which is used for collectingthe performance parameters of the internal combustion engine andcalculating the target supplied amount of urea in the exhaust system andfurther for determining the starting and finishing of the time points;the said urea storage device(3) is provided for storing the urea; thesaid compressed air supply device (2) is connected to the mainpipeline(7); the said compressed air control device(4) is installed atthe point where the compressed air supply device(2) is connected to themain pipeline(7), and the said compressed air control device(4)communicates with the electronic control unit(1) to control the flowrate of the compressed air sprayed into the main pipeline(7); a throughhole is formed in the middle section of the main pipeline(7); the twoends of the urea pipeline(8) is connected to the said urea storagedevice(3) and the through hole respectively; the said metering pump orthe metering valve(5) is installed to the urea pipeline(8) andcommunicates with the electronic control unit(1), which controls thevolume of the urea flowed into the main pipeline(7) from the ureastorage device(3); the outlet of the main pipeline(7) extends into theexhaust system; the said spray nozzle(6) is installed at the said outletof the main pipeline(7) so that the urea is introduced into the exhaustsystem by spray; the urea is mixed with the compressed air in the mainpipeline(7); wherein the said device further comprises an urea controldevice(9), which is installed to the main pipeline(7), and communicateswith the electronic control unit(1); the said urea control device(9) isprovided, when the urea is controlled to enter the exhaust system, thecompressed air is provided into the main pipeline(7), so that the ureain the main pipeline(7) will enter into the spray nozzle(6) by thecompressed air and further be injected into the exhaust system in thespay-like form; when the urea is controlled to be held from entering theexhaust system, the compressed air is provided into the spray nozzle(6)without passing through the main pipeline(7), causing the urea in themain pipeline(7) to be stopped entering the spray nozzle(6) and stoppedentering the exhaust system.
 2. The device for adjusting and controllingthe actual supplied amount of urea entering an exhaust system accordingto claim 1, wherein the said urea control device(9) comprises athree-way valve(94) and an branch airway(95); the said three-wayvalve(94) is installed to the section of the main pipeline(7) betweenthe compressed air control device(4) and the through hole; the inlet ofthe three-way valve(94) is connected to the compressed air controldevice(4) while the first outlet thereof is connected to the mainpipeline(7) and the second outlet thereof is connected to an end of thesaid branch airway(95); the other end of the branch airway(95) isconnected to the main pipeline(7), the connecting points are locatedbetween the urea pipeline(8) and the spray nozzle(6); the three-wayvalve(94) communicates with the electronic control unit(1); when theurea is controlled to enter the exhaust system, the three-way valve(94)connects the compressed air supply device(2) to the main pipeline(7),allowing the compressed air to be provided into the main pipeline(7);when the urea is controlled to be stopped entering the exhaust system,the three-way valve(94) connects the compressed air supply device(2) tothe branch airway(95), allowing the compressed air to enter the spraynozzle(6) through the branch airway(95).
 3. The device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem according to claim 1, wherein, the said urea control device(9) isprovided, when the urea is controlled to be stopped entering the exhaustsystem, the compressed air is changed to be prevented from entering thespray nozzle(6), so that the urea will not be entered into the spraynozzle(6) and be stopped entering into the exhaust system.
 4. The devicefor adjusting and controlling the actual supplied amount of ureaentering an exhaust system according to claim 3, wherein the said ureacontrol device(9) comprises a control valve(91); the said controlvalve(91) is installed to the main pipeline(7) between the ureapipeline(8) and the spray nozzle(6); the control valve(91) communicateswith the electronic control unit(1), which switches on and off theconnection between the main pipeline(7) and the spray nozzle(6) byswitching the control valve(91) to an open position or to a closeposition.
 5. The device for adjusting and controlling the actualsupplied amount of urea entering an exhaust system according to claim 3,wherein the said urea control device(9) further comprises a bypasschannel(92) and a bypass control valve(93); the said bypass channel(92)is connected to the main pipeline(7) with the connecting point locatedbetween the urea pipeline(8) and the spray nozzle(6); the said bypasscontrol valve(93) is installed to the bypass channel(92) andcommunicates with the electronic control unit(1), the electronic controlunit (1) switches the bypass control valve(93) to an open position forallowing the compressed air to enter the external atmosphere through thebypass channel(92) and switches the bypass control valve (93) to a closeposition for allowing the compressed air to enter the spray nozzle(6).6. The device for adjusting and controlling the actual supplied amountof urea entering an exhaust system according to claim 5, wherein theconnecting point of one end of the bypass channel(92) connected to themain pipeline(7) is located the upstream of the control valve(91); byswitching the control valve(91) to the close position and the bypasscontrol valve(93) to the open position, the compressed air is allowed toenter the bypass channel(92); whereas by switching the control valve(91)to the open position and the bypass control valve(93) to the closeposition, the compressed air is allowed to enter the spray nozzle(6). 7.The device for adjusting and controlling the actual supplied amount ofurea entering an exhaust system according to claim 5, wherein the otherend of the bypass channel(92) is further connected to the urea storagedevice(3); by switching the bypass control valve(93) to the openposition, the compressed air is allowed to enter the urea storagedevice(3) through the bypass channel(92).
 8. A method provided foradjusting and controlling the actual supplied amount of urea entering anexhaust system, wherein the said method comprises: Step 1: collectingthe performance parameters of the exhaust system and the internalcombustion engine, and calculating the target supplied amount of ureaentered into the exhaust system and further determining the starting andfinishing time point; Step 2: the compressed air supply device(2)providing the compressed air into the main pipeline(7), while the ureastorage device(3) providing the aqueous urea into the main pipeline(7)through the urea pipeline(8), so that the urea and the compressed airare mixed in the main pipeline(7); both the provided volume of the ureaand the flow rate of the compressed air are determined according to thetarget supplied amount of urea; Step 3: by referring to the startingtime point, when the urea is controlled to enter the exhaust system, thecompressed air is provided into the main pipeline(7) so that the urea inthe main pipeline(7) is fed into the spray nozzle(6) by the compressedair and further provided into the exhaust system in the spray-like form;by referring to the finishing time point, when the urea is controlled tobe stopped entering the exhaust system, the compressed air is providedinto the spray nozzle(6) without passing through the main pipeline(7),so that the urea in the main pipeline(7) is stopped to be fed into thespray nozzle(6) and further stopped entering into the exhaust system. 9.The method provided for adjusting and controlling the actual suppliedamount of urea entering an exhaust system according to claim 8, whereinthe said Step 3 further comprises: when the urea is controlled to enterthe exhaust system, the three-way valve(94) connects the compressed airsupply device(2) to the main pipeline(7), allowing the compressed air toenter the main pipeline(7); when the urea is controlled to be stoppedentering the exhaust system, the three-way valve(94) connects thecompressed air supply device(2) to the branch airway(95), allowing thecompressed air to enter the spray nozzle(6) through the branchairway(95).
 10. The method provided for adjusting and controlling theactual supplied amount of urea entering an exhaust system according toclaim 9, wherein when the target supplied amount of urea is below thepre-set threshold, the three-way valve (94) is controlled to connect tothe main pipeline(7) intermittently so that the compressed air isprovided into the main pipeline(7) intermittently, causing the remainedurea in the main pipeline(7) to enter the spray nozzle(6).
 11. Themethod provided for adjusting and controlling the actual supplied amountof urea entering an exhaust system according to claim 8, wherein thesaid Step 3 is replaced by following: when the urea is controlled toenter the exhaust system, the compressed air is provided into the mainpipeline(7) by referring to the starting time point, so that the urea inthe main pipeline(7) is fed into the spray nozzle(6) by the compressedair and further provided into the exhaust system in the spray-like form;when the urea is controlled to be stopped injecting into the exhaustsystem, the compressed air is prevented from entering the spraynozzle(6), so that the urea is stopped being fed into the spraynozzle(6) and further into the exhaust system.
 12. The method providedfor adjusting and controlling the actual supplied amount of ureaentering an exhaust system according to claim 11, wherein the said Step3 comprises installing the control valve(91) to the main pipeline(7);the control valve(91) is shifted between an open position and a closeposition to switch on and off the connection between the mainpipeline(7) and the spray nozzle(6).
 13. The method provided foradjusting and controlling the actual supplied amount of urea entering anexhaust system according to claim 11, wherein the said Step 3 furthercomprises installing a bypass channel(92) and a bypass control valve(93)outside the pipeline; when the bypass control valve(93) is shifted tothe open position, the compressed air is allowed to enter the externalatmosphere through the bypass channel(92), whereas when the bypasscontrol valve(93) is shifted to the close position, the compressed airis allowed to enter the spray nozzle(6).
 14. The method provided foradjusting and controlling the actual supplied amount of urea entering anexhaust system according to claim 13, wherein the said Step 3 furthercomprises that the connecting point of the bypass channel(92) with themain pipeline(7) is located at the upstream of the control valve(91); byswitching the control valve(91) to the close position and the bypasscontrol valve(93) to the open position, the compressed air is allowed toenter the bypass channel(92); whereas by switching the control valve(91)to the open position and the bypass control valve(93) to the closeposition, the compressed air is allowed to enter the spray nozzle(6).15. The method provided for adjusting and controlling the actualsupplied amount of urea entering an exhaust system according to claim13, wherein the said Step 3 further comprises that the other end of thebypass channel(92) is further connected to the urea storage device(3);by switching the bypass control valve(93) to the open position, thecompressed air is allowed to be fed into the urea storage device(3)through the bypass channel(92).
 16. The device for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem according to claim 4, wherein the said urea control device(9)further comprises a bypass channel(92) and a bypass control valve(93);the said bypass channel(92) is connected to the main pipeline(7) withthe connecting point located between the urea pipeline(8) and the spraynozzle(6); the said bypass control valve(93) is installed to the bypasschannel(92) and communicates with the electronic control unit(1), theelectronic control unit (1) switches the bypass control valve(93) to anopen position for allowing the compressed air to enter the externalatmosphere through the bypass channel(92) and switches the bypasscontrol valve (93) to a close position for allowing the compressed airto enter the spray nozzle(6).
 17. The method provided for adjusting andcontrolling the actual supplied amount of urea entering an exhaustsystem according to claim 12, wherein the said Step 3 further comprisesinstalling a bypass channel(92) and a bypass control valve(93) outsidethe pipeline; when the bypass control valve(93) is shifted to the openposition, the compressed air is allowed to enter the external atmospherethrough the bypass channel(92), whereas when the bypass controlvalve(93) is shifted to the close position, the compressed air isallowed to enter the spray nozzle(6).